ABSTRACT
With the growing application of high strength steel, as API 5L X80, for pipelines in the oil industry, and related geothermal energy generation plants, comes the concern about the risks involving hydrogen diffusion and hence, embrittlement due to severe operational conditions and corrosive environment containing hydrogen sulphide (H2S). Although many efforts have been made to predict and understand those phenomena, the mechanisms involving H2S corrosion combined with applied strain are still not entirely understood. In addition, the growth of iron sulphides scales can influence on the diffusion process. This study investigates the behaviour of the API X80 steel in relation to hydrogen absorption in solutions with different concentrations of H2S, at static and tensile test conditions. It aims to evaluate hydrogen embrittlement susceptibility of the steel by means of hydrogen permeation and slow strain rate tests. Furthermore, the present work seeks out to evaluate, particularly in this embrittlement process, the conditions of iron sulphide layer forming and stability in different solutions of sodium thiosulphate, as well as the film influence as a protective barrier to hydrogen entry. Investigations using electrochemical impedance spectroscopy and surface analysis by SEM, EDS and XRD indicated that exists a relationship between different concentrations of H2S, scale formation and its barrier protectiveness to hydrogen generation and uptake.
INTRODUCTION
Corrosion is one of the biggest and most costly problems in the oil industry, which has synergism with geothermal fluid used for energy production. One fifth of the worldwide steel production is destined to replace the loss caused by corrosion and the direct and indirect costs with corrosion can reach 4% of the GDP in developed countries.1
Due to the high demand in the flow of gas, oil and its derivatives, rises a need to develop high strength steels allied to a high tenacity and adequate weldability. This development is needed as an alternative for costs reductions on building and maintaining the pipelines and offshore structures, making possible the reduction of its wall thickness without modifying the operational conditions.
